New c u cable extension

[JohnW2]

As clearly stated I didn't look at makes.... Your investigations have been different ...

As I wrote, we have been addressing different questions by our'searches', and may well both the correct in our tentative conclusions.

You could be right in suggesting that at least 50% CUs in service have the main switch on the left, but, even if that is the case, I also still might be right in suggesting that only a small minority of available brands have that configuration.

 

[ebee]

I cannot see how lagging/leading might cause a trip, unless combined with some other fault on the immersion heater.

Possibly, the neutral breaking leading, combined with some leakage to earth, in the element, close to the neutral end of the element?

I think it was thought to be a possible one of the contributing factors because another factor or three was present such as E to N ins res or reactance or a capacative/inductive affect or something at the same time.
As said the change of DP switch completely curred the problem which might have been present for a very long time and only became apparent when switched off after years of being completely in circuit.

This was the broad concensus on this forum, the IET forum, at night school and a few of my peers.